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In many practical applications, it is always not necessary to analyse the complete circuit. To analyse the circuit, the voltage,current or power in only one resistance in that circuit is highly enough. To find the current in a resistor or a load, thevenin's theorem is quite useful.
Thevenin's theorem states that for the purpose of determining the current in a resistor, RL connected across two terminals of a network which contains sources of emf and resistors, the network can be replaced by a single source of emf (ETH) and a series resistor (RTH), to find the current passing through the load RL
Remove the load RL between the circuit terminals A an B.step 2:
Calculate the open-circuit voltage(Voc = Eth) which appears across terminals A and B, when they are open i.e) when (RL) is removed.step 3:
Short circuit the battery and find the Thevenin resistance RTH of the network as seen from the terminals A and B.step 4:
Connect RL back across the terminals A and B from where it was temporarily removed earlier.
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